I'll take a stab at this one.
5 Probably Black Ops 2?
There were so many worthy contenders for this honorary spot. Nobody really cares about the game that just barley made it on the list and between BLOPS 2, RE6, Inversion, MOH Warfighter Silent Hill HD and loads of other shit how can I even say any of those games are worse than one another. Am I right? So congratulations Black Ops 2! I personally disliked you more than all the other crap games that weren't objectively bad enough to make it any higher up on the list.
4 Amy
Most people forget that January was part of 2012. Fortunately there was something bad enough to keep January on my mind when coming up with games for this list. Maybe I'm being a little unfair because Amy was supposed to be a horror game, and be honest, is there anything more horrifying than a game this bad actually getting released? (Oh yeah the other 3 games on this list) It's unplayable, and all the other words I could use to describe Amy are either synonyms of unplayable or just swears. There are spelling errors in the subtitles. Just with the knowledge that the QA team couldn't be bothered to spell check the subtitles can you really expect them to catch even one of the innumerable bugs?
3 Assassin's Creed 3
There comes a time when enough becomes enough, and for the Assassin's Creed series that was somewhere around the time Revelations got released. Even at that point in the series the game was already struggling under the weight of all the pointless shit thrust upon you. So what does Ubisoft do? They add more stuff and they make it more pointless.
Talk about a slow start, It's not even like I'm opposed to slow starts, that can be an excellent tool to draw the audience in and make them care about the characters before introducing the plot, but in AC3's case the slow start is just boring and ultimately pointless because Connor is such an unlikeable twat we can't care about him or anything related to him. And I think the game is right with me on this because every main mission is basically just the polar opposite of the last mission you did, rendering everything Connor does moot before forcing another insufferable Desmond section down our throats.
2 Dishonored
There was a very specific moment when Dishonored lost me, not like it wasn't loosing me from the start, but I'll get to that in a minute. Mechanically there's not a lot to complain about in Dishonored. But Games aren't a purely mechanical medium, and the minds behind Dishonored seem to be confused by that notion. They put a lot of effort into making the city very...uh, cultural. Between the decor and all the flavor text you can read to the costume designs and art direction (It's all still grey but it's interesting grey) but then they populate the entire place with emotionless zombies who spout off drab, poorly acted, badly written dialog that makes Oblivion look like Shakespeare. So as much as you might care about the history and city and culture you have to either experience it through walls of text or the emotionless populous. (And that applies to the main characters as well. There's not a single emotion or coherent motivation to be had through out the whole game)
The Morals are warped as fuck. Here's the drill. The only bad thing you can do in Dunwall is to kill. Everything else is basically smiled upon by the fates. But the rub comes in when you think about the mechanics of the game. The combat system is functional, unique, and interesting to use. Where most games would have you wade into the situation guns/swords blazing in Dishonored setting up elaborate Rube Goldberg contraptions is just as effective and more fun to watch play out. But the game doesn't want you to do that. No sir, no murder for you, or else you'll get the bad end with no supper. It's not like you couldn't just re load a previous save and slaughter everyone in sight. But the fact that you have to resign your self to not playing the game in order to have any fun with it is mindbogglingly. Especially because the stealth stuff they actually expect you to do is so dull...
So Dishonored was on the fast track to be my most mediocre game of 2012 because "one step forward one step back" still leaves you at square one. But then you get to the actions you're called upon to preform in order to get story progression.
So to get back to what I said earlier about murder bad, everything else sunshine and butterflies. You run in to the perplexing situation where the bad option is to kill someone and the good option is to torture, dismember, disfigure and leave him to suffer in agony for the rest of his life... well uh... I'm a little uncomfortable with this now. maybe it gets better? What's another "Moral" choice you have to make? Bad option Kill a woman. Good option drug her, tie her up, sell her up the river to a creepy rapist stalker. NOPE! I'm out. I wash my hands of this morally repugnant piece of filth. Get out of my life and get wiped from my brain you disgusting swill.
1 Mass Effect 3
This is the only instance where I've ever wanted to see a game developer punished. I loved the first 2 Mass Effect games with a passion, and honestly didn't even come into Mass Effect 3 with very high hopes in a desperate attempt to abate some disappointment when it didn't live up to the unreal expectations the first two games set for it. And it still managed to disappoint me at every turn. With in 5 minutes of starting the game it managed to change what Shepard looked like, The first spoken line of dialog was a plot hole, and it undid THE MOST IMPORTANT DECISION YOU MADE IN THE FIRST GAME!
And this is even before you get the push any buttons on the controller (Keyboard, whatever). Once you do get to push buttons you find out just how broken the game really is. The controls don't work, like not even a little. The amount of luck involved is something as integral to the gameplay as taking cover is atrocious. You might sprint into it, you might do a barrel roll in front of it, you might vault over it, or you might actually take cover. And if there's an intractable object in Shep's general vicinity there's a pretty fair shot s/he might just walk over and pick it up in the middle of a firefight.
But enough about the controls they aren't nearly the worst part of a game that was supposed to be the epic conclusion to a massively player controlled narrative. Every single choice you made in the previous two games is ignored because apparently Bioware want's to start telling stories instead of letting the player fill in the blanks on the general "Hero's journey" plot line. (Which is what they've been doing since the start)
Trying to impose a narrative over 2 games worth of player choice would be a tall order if that was what they even bothered to do, in stead they just decided to scrap the player choice all together and just make up new personalities, back-stories and motivations for all the characters on the fly, because apparently Bioware didn't even want to be held accountable to stuff that they them selves wrote that the player didn't even have any control over in the first place.
Every element that they (Arbitrarily) decided couldn't be hand waived or ret-conned away Like Romances, results of loyalty missions, characters that did or didn't survive until the third game just went mostly unmentioned outside maybe one or two lines that are left as vague as possible for the benefit of people who didn't play the first two games.
That covers it for how ME3 ruined ME's 1 and 2, let's talk about how it's bad on it's own merits, why don't we. As part of being an epic conclusion there must have been some discussion about the main conflict. An ancient unstoppable evil force. How do you stop one of those? With a Dues Ex Machina of course, that's pretty standard fantasy fair right? (Even though this is SciFi) So how was it handled? (Obviously not well, otherwise it wouldn't be the worst game of the year)
The Crucible is the rock paper scissors of bad writing. It's not explainable, the characters constantly bang on about it, and every single new piece of information reviled about it contradicts the last one.
Some simple reverse engineering of some exposition can prove beyond a shadow of a doubt that none of it makes any fucking sense.
The Crucible is a power source.
The Crucible's function is to change the Catalyst.
The Catalyst is in the Citadel.
Integration with the Citadel was added to the Crucibles design hundreds of cycles after it was first invented.
So...What did the first civilization that started construction intend to do with it?
Why were they building a giant battery if they didn't intend to hook it up to anything?
The Reapers built the Citadel.
The Keepers maintain the Citadel.
The Keepers communicated with the Reapers every cycle up until the Prothean cycle.
So if one of the pre-Prothean cycles tried to hook up the Crucible to the Citadel the Reapers would have known about it.
And that's all just based on putting two and two together from lines in the game Lines that were drilled home with vast importance.
When a series that started as a close personal character drama turns into a broad scope indecipherable exposition dump at the expense of everything the first two games spend well on 100 hours building up that's basically proof that no one involved in the production of this game gave a shit.